Gas Desorption Rate of Coal Seams in Zonguldak Coal Basic As an Indicator of Outburst Proneness Olgun Esen Istanbul Technical University
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University of Wollongong Research Online Coal Operators' Conference Faculty of Engineering and Information Sciences 2018 Gas Desorption Rate of Coal Seams in Zonguldak Coal Basic as an Indicator of Outburst Proneness Olgun Esen Istanbul Technical University Abdullah Fisne Istanbul Technical University Gündüz Ökten Istanbul Technical University Dennis J. Black CoalGAS Publication Details Olgun Esen, Abdullah Fisne, Gündüz Ökten and Dennis Black, Gas Desorption Rate of Coal Seams in Zonguldak Coal Basic as an Indicator of Outburst Proneness, Proceedings of the 18th Coal Operators' Conference, Mining Engineering, University of Wollongong, 264-272. Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] 2018 Coal Operators Conference GAS DESORPTION RATE OF COAL SEAMS IN ZONGULDAK COAL BASIN AS AN INDICATOR OF OUTBURST PRONENESS 1 2 3 Olgun Esen , Abdullah Fisne , Gündüz Ökten , Dennis Black4 ABSTRACT: Outburst is a significant hazard in underground coal mining and may be expressed as a violent ejection of coal and gas from the mining face. Greatest risk of outburst is during initial intersection of an unmined coal seam and during development mining of the coal seam in close proximity to geological disturbances. Outburst events have been reported during underground mining operations in over 18 countries, including Turkey, for over 150 years. In the Zonguldak Coal Basin, located on the Black Sea coast of North West Turkey, 90 outbursts were recorded over 44 years, between 1969 and 2013, resulting in 374 fatalities. To protect the mine workings from the outburst hazard, the outburst indicators, ∆P0-60, ∆Pexpress and the KT index, have been investigated to evaluate potential application to predict outburst prone areas. The study of 166 coal samples collected from the three (3) coal seams, Acilik, Sulu and Cay seams, mined at Kozlu and Karadon collieries in the Zonguldak Coal Basin, found the results of ∆P0-60, ∆Pexpress and the KT index ranged between 2 to 26 mmHg, 0.16 to 0.76 bar, and 0.57 to 0.79 respectively. These results were compared with threshold limit values reported in previous studies to identify areas of potential increased outburst risk. INTRODUCTION An outburst is a sudden release of gas and coal under pressure from a working face area (Black, 2011). Various theories have been presented regarding factors that contribute to the occurrence of coal and gas outbursts. Factors that may affect outburst potential include tensile strength of coal, gas emission rate, gas pressure gradient, moisture content and the magnitude of local stresses (Lama, 1995). Specifically, high levels of seam gas near geological structures have been identified as a major contributing factor in the coal and gas outburst phenomenon (Lama, 1995). In Turkey, methane (CH4) is the dominant seam gas and has been associated with past outburst events. Carbon dioxide (CO2) and variable concentrations of CH4 and CO2, in combination with the ejection of fine coal particles, have also been released in outburst events reported in Australia, Canada, China, Czech Republic, France, Poland (Beamish and Crosdale, 1998; Lama and Bodziony, 1998; Lama and Saghafi, 2002; Liu et al., 2008; Aziz et al., 2011). Despite much research, the coal and gas outburst phenomenon is not well understood and many researchers continue to investigate the occurrence mechanism and prediction techniques. In Turkey, coal and gas outburst events were first recognised and reported in 1969 and in the 44 years to 2013, 90 outburst events were recorded, all events occurring in the Karadon and Kozlu collieries located in the Zonguldak Coal Basin. Fisne and Esen (2014) reported the highest number of outbursts occurred during mining of three seams at the two collieries; 20 outburst events in the Acilik seam, 15 outbursts in the Cay seam, and 13 outbursts in the Sulu seam. The two methods used for outburst prevention in Turkish coalmines are (a) local drilling of boreholes to reduce gas pressure, and (b) protective seam mining. However, further work is needed to identify accurate and reliable methods to locate areas of increased outburst risk, where outburst prevention efforts can be concentrated. Four factors are considered to have the greatest impact on outburst propensity, the most significant being gas content/gas 1 Research and Teaching Asst, Istanbul Technical University. Email: [email protected] Tel: +90 212 285 6361 2 Associate Professor, Istanbul Technical University. Email: [email protected] Tel: +90 212 285 6363 3 Prof. Dr. Istanbul Technical University. Email: [email protected] Tel: +90 212 285 6340 4 University of Wollongong; Consultant, CoalGas. Email: [email protected] Tel: +61 401 999 542 University of Wollongong, February 2018 264 2018 Coal Operators Conference pressure, have been presented as an outburst risk matrix by Black (2017) and Black et al., 2009 (Figure 1). Figure 1: Outburst risk matrix (Black, 2017). Bodziony and Lama (1996) described outburst prediction indices, such as ΔP0-60, ΔPexpress, and the KT index, used with varying levels of effectiveness by different countries, to identify areas of increased outburst risk. While these prediction indices, related to initial gas desorption, must be used in conjunction with other parameters such as coal properties, coal seam gas content and stress conditions, to fully assess outburst risk, it is important to recognise and accept the importance of gas desorption ratefrom coal while investigating the outburst prone coal seams. In this study, ΔP0-60, ΔPexpress index, and KT index are determined for coal samples collected from the Acilik, Sulu and Cay coal seams in Kozlu and Karadon collieries and the results are assessed to identify potential outburst prone conditions in each seam. STUDY AREA Zonguldak Coal Basin, located on the Black Sea Coast (Figure 2), is the only bituminous coal basin in Turkey. Zonguldak Coal Basin is the main part of the Upper Carboniferous bituminous coal basin, much of the bituminous coal mining has thus been concentrated in the Zonguldak Basin (Karayigit, 2001). The coal seams are located in a Carboniferous deltaic sequence of Westphalian-A age. The coalfield has a complex and hard geological condition, first by Hercynian and later by Alpine orogenesis resulting in folding and faulting of strata (Okten, et al., 1995). The Carboniferous coal-bearing sequence of the Zonguldak basin contains the Namurien Alacaagzi Formation, Westphalian-A Kozlu Formation and Westphalian B-D Karadon Formation (Gurdal and Yalcin, 2000). University of Wollongong, February 2018 265 2018 Coal Operators Conference Figure 2: Geological setting of the Zonguldak coal basin (from Hosgormez, 2007). Mining activities in the basin started in 1848 and have continued in the region for over 160 years. Several national and international companies operate coal mines in the basin. The mining area is 6885 km2 and mining depth continues to increase. Coal is produced from five collieries, shown in Figure 3, Armutcuk, Kozlu, Uzulmez, Karadon and Amasra that are operated by the Hard Coal Agency of Turkey (TTK). In Kozlu colliery, mine workings have extended out below the Black Sea and have reached depths of 1200 metres. The saleable production is relatively low by Australian standards, totalling 948,573 tonnes in 2015, 908,107 tonnes in 2016, 2017 production year-to-date is approaching 830,000 tonnes. TTK employs 9,000 people and 6,000 of those employees work in the underground mines (TTK Annual Report, 2017). Increasing gas content and high gas concentration in working places has been identified as a contributing factor to reduced coal production from the TTK collieries. While the Acilik, Sulu and Cay seams are recognised as having the highest propensity for coal and gas outbursts, they contain the highest quality coal and are the target for intensive coal production in the basin. Figure 3: Location of the Zonguldak Coal Basin. METHODOLOGY OF GAS DESORPTION RATEINDICES Gas desorption rate is an important parameter to consider in assessing outburst proneness of the coal seams (Williams, 1997). A variety of sorption/desorption indices have been used in different countries for prediction of coal outburst risk (Lama and Bodziony, 1996). These indices provide a measure of initial gas desorption, typically from small samples of fine coal particles, and the index values must be related to other factors such as structure of coal, gas University of Wollongong, February 2018 266 2018 Coal Operators Conference content, and stress, to thoroughly assess outburst risk. The following three indices have been investigated: • KT index • ΔP0-60 index; and • ΔPexpress index. KT index This index is a measure of the change in desorption rate of a coal sample. Plotting measurements of gas desorption (cm3/min.kg) relative to desorption time (min) on a ln-ln scale, the slope of the curve represents the KT value. The method of sampling consists of drilling holes and collecting fractions of particles in the range 0.40 to 0.63 mm and the mass of the sample depends upon the capacity of the equipment. Lama and Bodziony (1996) suggest the critical value KT < 0.645 ± 0.035 is considered normal and for outburst conditions, KT should be at least 0.75. Lama and Bodziony also suggest the critical KT value relates to a gas content of 9.0 m3/t. Ökten (1983) proposed the KT index categories, listed in Table 1, to classify outburst prone coal seams. Table 1: KT index classification for coal and gas outbursts. Category KT Range Description 1 0.75 to 0.82 Potential of Outburst 2 0.82 to 0.88 Risk of Outburst 3 > 0.88 High Risk of Outburst ΔP0-60 index Lama and Bodziony (1996) referred to work of , Ettinger et al. from 1953, whichpresented an alternative to measuring gas desorption as a percentage of gas sorbed at 1 atm pressure, which involved measuring gas pressure build up in an enclosed chamber of definite dimensions, expressed as “gas emission index”.